To characterise the profile of lymphopenia that occurs following initiation of cladribine tablets in patients who have switched from lymphocyte depleting or sequestering agents, and evaluate short term efficacy and safety profiles in this cohort.

Of the 50 patients who have transitioned to cladribine tablets from lymphocyte targeted therapies, the effect on lymphocytes remained predictable, despite initiating cladribine tablets at or around the lower limit of normal. The magnitude of reduction in lymphocytes for patients switching from fingolimod to cladribine was reduced, perhaps owing to parallel but opposing processes, as lymphocytes egress from the lymph nodes. Conversely, in patients transitioning from natalizumab the magnitude of lymphocytosis in relative terms was increased. Reported AEs were comparable to those reported in the literature.  

Oral cladribine has a predicable effect on lymphopenia. The magnitude of the effect differs depending on baseline levels, with the overall nadir similar.